linux-kernel - Re: [PATCH] xfs: mark sb

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Date:   Fri, 25 May 2018 22:18:16 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Eric Sandeen <sandeen@...hat.com>,
        Martin Sebor <msebor@...il.com>,
        Brian Foster <bfoster@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        Eric Sandeen <sandeen@...deen.net>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: mark sb_fname as nonstring

On Fri, May 25, 2018 at 6:52 PM, Christoph Hellwig <hch@...radead.org> wrote:
>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>> index 84fbf164cbc3..eb79f2bc4dcc 100644
>> --- a/fs/xfs/xfs_ioctl.c
>> +++ b/fs/xfs/xfs_ioctl.c
>> @@ -1819,12 +1819,12 @@ xfs_ioc_getlabel(
>>       BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
>>
>>       spin_lock(&mp->m_sb_lock);
>> -     strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname));
>> +     strncpy(label, sbp->sb_fname, XFSLABEL_MAX);
>>       spin_unlock(&mp->m_sb_lock);
>
> Hmm, shouldn't we just do a memcpy here?

I thought about that as well, but decided that strncpy()'s zero-padding
is better here than padding with potentially random contents of the user
space stack.

> Also given that the kernel never even looks at sb_fname maybe
> we can turn into an array of unsigned chars to escape those string
> warnings?

I don't think that makes a difference to gcc.

        Arnd